Molecular mechanisms and microRNAs in osteosarcoma pathogenesis

This review summarizes data on microRNA (miRNA) genomic organization, biogenesis, and functions in carcinogenesis. The roles of key genes and regulatory miRNAs in molecular mechanisms and signaling pathways involved in the development of osteosarcoma, the most aggressive type of bone tumor striking mainly in adolescence and early adulthood, are discussed in detail. The most critical pathways in osteosarcoma pathogenesis are the Notch, Wnt, NF-κB, p53, PI3K/Akt, and MAPK pathways. The balance between cell survival and apoptosis is determined by the Wnt and NF-κB pathways, as well as by the ratio between the activities of the MAPK and PI3K/Akt pathways. Several miRNAs (miR-21, -34a, -143, -148a, -195a, -199a-3p, -382) regulate multiple target genes, pathways, and processes essential for osteosarcoma pathogenesis. Data on the key genes and regulatory miRNAs involved in metastasis and tumor cell response to drug treatment are presented. Possible applications of miRNA in osteosarcoma diagnostics and treatment are discussed.     

Polygonatum cyrtonema lectin, a potential antineoplastic drug targeting programmed cell death pathways

Polygonatum cyrtonema lectin (PCL), a mannose/sialic acid-binding plant lectin, has recently drawn a rising attention for cancer biologists because PCL bears remarkable anti-tumor activities and thus inducing programmed cell death (PCD) including apoptosis and autophagy in cancer cells. In this review, we focus on exploring the precise molecular mechanisms by which PCL induces cancer cell apoptotic death such as the caspase-dependent pathway, mitochondria-mediated ROS–p38–p53 pathway, Ras–Raf and PI3K–Akt pathways. In addition, we further elucidate that PCL induces cancer cell autophagic death via activating mitochondrial ROS–p38–p53 pathway, as well as via blocking Ras–Raf and PI3K–Akt pathways, suggesting an intricate relationship between autophagic and apoptotic death in PCL-induced cancer cells. In conclusion, these findings may provide a new perspective of Polygonatum cyrtonema lectin (PCL) as a potential anti-tumor drug targeting PCD pathways for future cancer therapeutics.     

Phosphoinositide 3-OH kinase (PI3K) and PKB/Akt delay the onset of p53-mediated, transcriptionally dependent apoptosis.

The phosphoinositide 3-OH kinase (PI3K)-PKB/Akt signaling pathway has been shown to mediate both Ras- and cytokine-induced protection from apoptosis. In addition, apoptosis induced by the p53 tumor suppressor protein can be inhibited by Ras- and cytokine-mediated signaling pathways. It was therefore of interest to determine if the PI3K-PKB/Akt signaling pathway was capable of conferring protection from apoptosis induced by p53. We demonstrate in this report that constitutively active PI3K and PKB/Akt are capable of significantly delaying the onset of p53-mediated apoptosis. This was manifested as a delay in the kinetics of DNA degradation and cell death as well as a profound attenuation in the accumulation of cells with a sub-G(1) DNA content. Moreover, we found that this effect is mediated in the absence of changes in expression of Bcl-2, Bcl-Xl, and the pro-apoptotic protein Bax. Our results provide the first direct and unambiguous link between p53-mediated apoptosis and the PI3K-PKB/Akt signaling pathway.     

Siva is an apoptosis-selective p53 target gene important for neuronal cell death

p53 plays a central role in neuronal cell death resulting from acute injury or disease. To define the pathway by which p53 triggers apoptosis, we used microarray analysis to identify p53 target genes specifically upregulated during apoptosis but not cell cycle arrest. This analysis identified a small subset of targets highly selective for the p53 apoptotic response, including Siva, a proapoptotic protein whose function is not well understood. Siva's expression pattern suggests that it plays an instructive role in apoptosis, and accordingly, we demonstrate that Siva is essential for p53-dependent apoptosis in cerebellar granule neurons. In addition, we determine that endogenous Siva is associated with the plasma membrane and that Caspase-8 and Bid are important for neuronal apoptosis. Our studies highlight the participation of membrane signaling events in p53's apoptotic program in primary neurons and have significant implications for understanding the mechanisms underlying pathogenesis after neuronal injury and in neurodegenerative diseases.     

CDIP, a novel pro-apoptotic gene, regulates TNFalpha-mediated apoptosis in a p53-dependent manner

We have identified a novel pro-apoptotic p53 target gene named CDIP (Cell Death Involved p53-target). Inhibition of CDIP abrogates p53-mediated apoptotic responses, demonstrating that CDIP is an important p53 apoptotic effector. CDIP itself potently induces apoptosis that is associated with caspase-8 cleavage, implicating the extrinsic cell death pathway in apoptosis mediated by CDIP. siRNA-directed knockdown of caspase-8 results in a severe impairment of CDIP-dependent cell death. In investigating the potential involvement of extrinsic cell death pathway in CDIP-mediated apoptosis, we found that TNF-alpha expression tightly correlates with CDIP expression, and that inhibition of TNF-alpha signaling attenuates CDIP-dependent apoptosis. We also demonstrate that TNF-alpha is upregulated in response to p53 and p53 inducing genotoxic stress, in a CDIP-dependent manner. Consistently, knockdown of TNF-alpha impairs p53-mediated stress-induced apoptosis. Together, these findings support a novel p53 --> CDIP --> TNF-alpha apoptotic pathway that directs apoptosis after exposure of cells to genotoxic stress. Thus, CDIP provides a new link between p53-mediated intrinsic and death receptor-mediated extrinsic apoptotic signaling, providing a novel target for cancer therapeutics aimed at maximizing the p53 apoptotic response of cancer cells to drug therapy.     

Regulation of FOXO3a/beta-catenin/GSK-3beta signaling by 3,3'-diindolylmethane contributes to inhibition of cell proliferation and induction of apoptosis in prostate cancer cells

Previous studies from our laboratory have shown anti-proliferative and pro-apoptotic effects of 3,3'-diindolylmethane (DIM) through regulation of Akt and androgen receptor (AR) in prostate cancer cells. However, the mechanism by which DIM regulates Akt and AR signaling pathways has not been fully investigated. It has been known that FOXO3a and glycogen synthase kinase-3beta (GSK-3beta), two targets of activated Akt, interact with beta-catenin, regulating cell proliferation and apoptotic cell death. More importantly, FOXO3a, GSK-3beta, and beta-catenin are all AR coregulators and regulate the activity of AR, mediating the development and progression of prostate cancers. Here, we investigated the molecular effects of B-DIM, a formulated DIM with higher bioavailability, on Akt/FOXO3a/GSK-3beta/beta-catenin/AR signaling in hormone-sensitive LNCaP and hormone-insensitive C4-2B prostate cancer cells. We found that B-DIM significantly inhibited the phosphorylation of Akt and FOXO3a and increased the phosphorylation of beta-catenin, leading to the inhibition of cell growth and induction of apoptosis. We also found that B-DIM significantly inhibited beta-catenin nuclear translocation. By electrophoretic mobility shift and chromatin immunoprecipitation assays, we found that B-DIM inhibited FOXO3a binding to the promoter of AR and promoted FOXO3a binding to the p27(KIP1) promoter, resulting in the alteration of AR and p27(KIP1) expression, the inhibition of cell proliferation, and the induction of apoptosis in both androgen-sensitive and -insensitive prostate cancer cells. These results suggest that B-DIM-induced cell growth inhibition and apoptosis induction are partly mediated through the regulation of Akt/FOXO3a/GSK-3beta/beta-catenin/AR signaling. Therefore, B-DIM could be a promising non-toxic agent for possible treatment of hormone-sensitive but most importantly hormone-refractory prostate cancers.     

Modulation of curcumin-induced Akt phosphorylation and apoptosis by PI3K inhibitor in MCF-7 cells

Curcumin has been shown to induce apoptosis in various malignant cancer cell lines. One mechanism of curcumin-induced apoptosis is through the PI3K/Akt signaling pathway. Akt, also known as protein kinase B (PKB), is a member of the family of phosphatidylinositol 3-OH-kinase regulated Ser/Thr kinases. The active Akt regulates cell survival and proliferation; and inhibits apoptosis. In this study we found that curcumin induces apoptotic cell death in MCF-7 cells, as assessed by MTT assay, DNA ladder formation, PARP cleavage, p53 and Bax induction. At apoptotic inducing concentration, curcumin induces a dramatic Akt phosphorylation, accompanied by an increased phosphorylation of glycogen synthase kinase 3β (GSK3β), which has been considered to be a pro-growth signaling molecule. Combining curcumin with PI3K inhibitor, LY290042, synergizes the apoptotic effect of curcumin. The inhibitor LY290042 was capable of attenuating curcumin-induced Akt phosphorylation and activation of GSK3β. All together, our data suggest that blocking the PI3K/Akt survival pathway sensitizes the curcumin-induced apoptosis in MCF-7 cells.     

Crosstalk between Phosphoinositide 3-kinase/Akt signaling pathway with DNA damage response and oxidative stress in cancer

The phosphatidylinositol 3-kinases (PI3K)/Akt signaling pathway is one of the well-characterized and most important signaling pathways activated in response to DNA damage. This review discusses the most recent discoveries on the involvement of PI3K/Akt signaling pathway in cancer development, as well as stimulation of some important signaling networks involved in the maintenance of cellular homeostasis upon DNA damage, with an exploration of how PI3K/Akt signaling pathway contributes to the regulation of modulators and effectors underlying DNA damage response, the intricate, protein-based signal transduction network, which decides between cell cycle arrest, DNA repair, and apoptosis, the elimination of irreparably damaged cells to maintain homeostasis. The review continues by looking at the interplay between cell cycle checkpoints, checking the repair of damage inflicted to the DNA before entering DNA replication to facilitate DNA synthesis, and PI3K/Akt signaling pathway. We then investigate the challenges the cells overcome to ameliorate damages induced by oxidative activities, for example, the recruitment of many pathways and factors to maintain integrity and hemostasis. Finally, the review provides a discussion of how cells use the PI3K/Akt signaling pathway to regulate the balance between these networks.     

PUMA与心肌细胞凋亡的研究进展

p53上调的凋亡调节物(p53 upregulated modulator of apoptosis,PUMA)是新近发现的一种具有促凋亡作用的p53靶基因.与以往发现的其他p53靶基因比较,PUMA在促凋亡作用中有两个重要的特点:一是PUMA几乎介导p53依赖的所有凋亡信号;二是PUMA不仅介导p53依赖的凋亡信号,而且还可以介导p53非依赖的凋亡信号.也就是说,尽管PUMA是p53靶基因,但是其在p53非依赖细胞凋亡中也发挥重要作用.由此可见,PUMA是一个强大的促凋亡因子.在心肌细胞,PUMA参与缺血/再灌注、内质网应激、阿霉素等多种刺激诱导的细胞凋亡.因此,PUMA在心肌细胞凋亡中发挥重要作用.     

4-Hydroxynonenal induces p53-mediated apoptosis in retinal pigment epithelial cells

4-Hydroxynonenal (4-HNE) has been suggested to be involved in stress-induced signaling for apoptosis. In present studies, we have examined the effects of 4-HNE on the intrinsic apoptotic pathway associated with p53 in human retinal pigment epithelial (RPE and ARPE-19) cells. Our results show that 4-HNE causes induction, phosphorylation, and nuclear accumulation of p53 which is accompanied with down regulation of MDM2, activation of the pro-apoptotic p53 target genes viz. p21 and Bax, JNK, caspase3, and onset of apoptosis in treated RPE cells. Reduced expression of p53 by an efficient silencing of the p53 gene resulted in a significant resistance of these cells to 4-HNE-induced cell death. The effects of 4-HNE on the expression and functions of p53 are blocked in GSTA4-4 over expressing cells indicating that 4-HNE-induced, p53-mediated signaling for apoptosis is regulated by GSTs. Our results also show that the induction of p53 in tissues of mGsta4 (−/−) mice correlate with elevated levels of 4-HNE due to its impaired metabolism. Together, these studies suggest that 4-HNE is involved in p53-mediated signaling in in vitro cell cultures as well as in vivo that can be regulated by GSTs.     

突变型p53与其合成致死基因的研究进展

恶性肿瘤的靶向治疗已经成为现阶段肿瘤治疗的热点。随着人们对癌基因认知的加深,借助合成致死的方法靶向治疗肿瘤已成为针对肿瘤特异性治疗的新策略。p53基因突变在肿瘤的形成和发展过程中具有重要作用。因此,了解肿瘤中与突变型p53基因有合成致死关系的靶基因的作用方式,有助于指导由突变型p53基因诱发肿瘤的个性化治疗。与突变型p53基因具有合成致死关系的靶基因可分为细胞周期调控基因和细胞非周期调控基因,文章综述了这两类靶基因与突变型p53基因如何构成合成致死作用以及此作用的现实意义。